Level sensors detect the level of substances that flow, including liquids, slurries, granular materials, and powders. Fluids and fluidized solids flow to become essentially level in their containers (or other physical boundaries) because of gravity whereas most bulk solids pile at an angle of repose to a peak. The substance to be measured can be inside a container. The level measurement can be either continuous or point values. Continuous level sensors measure level within a specified range and determine the exact amount of substance in a certain place, while point-level sensors only indicate whether the substance is above or below the sensing point. Generally the latter detect levels that are excessively high or low.
There are many physical and application variables that affect the selection of the optimal level monitoring method for industrial and commercial processes. The selection criteria can include one or more of the following: phase (liquid, solid or slurry), temperature, pressure or vacuum, chemistry, dielectric constant of medium, density (specific gravity) of medium, agitation (action), acoustical or electrical noise, vibration, mechanical shock, tank or bin size and shape. Also important are the application constraints, which may include: price, accuracy, appearance, response rate, ease of calibration or programming, physical size and mounting of the instrument, monitoring or control of continuous or discrete (point) levels.
Overview
Various methods and systems are provided to control a probe moving towards fluid held in a container. The probe is moved towards the fluid to take a sample of the fluid in the container. To take a sample, probe is actuated to hit the fluid surface and to pass the fluid surface by a predetermined distance. Capacitive sensing which incorporates the probe itself is used to support an approach engine for controlling the motion of the probe. The approach engine determines the speed of the probe based on capacitance measurements, and in some cases based on position information of the probe. The approach engine ensures the probe hits the surface of the fluid in the container in order to take a sample while ensuring the probe does not hit the bottom of the container.